Magnesium dry battery with anode contact protection

ABSTRACT

The external, nonreacting surface of the magnesium anode of a dry cell is covered by a protective coating to prevent impairment or loss of electrical contact with the adjacent cell of a battery which, it has been discovered, frequently results from limited but effective chemical action that takes place at this exposed surface and proceeds under presumably sealing barriers to undermine electrical contact with the adjoining cell.

United States Patent [7 21 Inventor Lloyd W. Eaton Cleveland, Ohio [21]Appl. No. 13,286 [22] Filed Feb. 24, 1970 [45] Patented Jan. 11, 1972[73] Assignee Clevite Corporation Cleveland, Ohio [54] MAGNESIUM DRYBATTERY WITH ANODE CONTACT PROTECTION 4 Clalms, 2 Drawing Figs.

[52] U.S.Cl 136/111, 1 136/133 [51] lnt.Cl ..H0lln21/00 [50] Field ofSearch 136/100, 1 l l, 133, 120

[56] References Cited UNITED STATES PATENTS 2,229,431 1/1941 Young136/1115 2,645,676 7/1953 Emeriat 136/1 1 1.7 2,745,894 5/1956 Nowotny136/111 2,880,259 3/1959 Nowotny 136/111 3,185,592 5/1965 Kirk et a1136/100M 3,255,048 6/1966 Comanor et a1. 136/100M 3,390,016 6/1968Nelson 136/100 M 3,525,647 8/1970 Strauss 136/1 1 1 PrimaryExaminerWinston A. Douglas Assistant Examiner-C. F. Lefevour Attorney-Darbo, Robertson & Vandenburgh ABSTRACT: The external, nonreactingsurface of the magnesium anode of a dry cell is covered by a protectivecoating to prevent impairment or loss of electrical contact with theadjacent cell of a battery which, it has been discovered, frequentlyresults from limited but effective chemical action that takes place atthis exposed surface and proceeds under presumably sealing barriers toundermine electrical contact with the adjoining cell.

PATENTED JAN! I I972 31634; 142

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MAGNESIUM DRY BATTERY WITH ANODE CONTAGT PROTECTION BACKGROUND ANDSUMMARY OF THE INVENTION part, to its great reactivity. By usingappropriate electrolytes l and inhibitors and by following specialtechniques in their manufacture, cells having cylindrical or flatmagnesium anodes have been successfully manufactured in largequantities.

As a matter of convenience and manufacturing efficiency, as well as thedifficulties involved in soldering to magnesium "surfaces, batteryintercell connections are advantageously made by means of a conductivethermoplastic material, such as the silver particle impregnated wax ofKurlandsky US. Pat.

. No. 2,666,803 This method of connecting the terminals of adjacentcells is especially useful in batteries consisting of stacks of flatcells; a small quantity of the conductive material placed between partsto be electrically connected which are normally pressed tightly togetherin the assembled battery serves the purpose.

The reliability of such batteries, especially after a period of storage,has been less than satisfactory. Many have been found to produceinadequate current, apparently the consequence of excessive resistancein the battery internal circuit, and frequently batteries are found tobe entirely dead although never used. It was discovered in the course ofa very thorough investigation, and subsequently confirmed, that thetrouble resulted from the undermining of the intercell connections atthe magnesium surfaces due to a corrosion of the exposed surfaces of theanodes which proceeded along under what had been assumed to be sealssurrounding the contacts. Apparently, such corrosion resulted from thepresence of moisture in the space between adjacent cells the presence ofwhich is practipally inevitable.

The object of this invention is to provide a method and means forpreventing the disabling undermining of intercell connections betweendry cells having magnesium anodes and thus greatly improve thereliability of magnesium cell batteries. More specifically, the objectof the invention is to provide effective protection of the exposedsurfaces of the magnesium anodes of the cells of a dry battery toprevent surface corrosion which, when carried far enough, impairs ordestroys the electrical connection of the magnesium anode with theintercell connecting element.

These and other objects and advantages of the invention will becomeapparent from the following description and the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is an exploded cross-sectionalview ofa single cell illustrating an exemplary embodiment of theinvention, and

FIG. 2 is a view of the cell of FIG. 1 taken at the line 22 thereof andshowing the magnesium anode with protective coating applied inaccordance with the invention.

DESCRIPTION OF A PREFERRED EMBODIMENT The dry cell and the partsthereof, as illustrated in FIG. 1, are, with the single exception to bedescribed below in detail, well known. The electrochemically activecomponents include anode l and cathode 2, the latter comprising a mix ofdepolarizing and conductive materials and a suitable electrolyte, suchas magnesium bromide solution, separated from each other by means of abibulous separator 3. A conductive carbon current collector 4 engagesthe surface of cathode 2 and the cell is enclosed and sealed within awrap composed of rubber hydrochloride films 5 and 6. A circular seal 7of asphalt or hot melt adhesive resin serves to seal the currentcollector 4 to the enclosing film encircling a hole 8 provided in thefilm for the intercell connecting material 9. Similarly, a circular seal10 serves to seal the anode to the film covering 6,

surrounding hole I I which is provided for access of the intercellconnecting material I2 to the anode.

Advantageously, a disc 13 of inert and nonconductive material is adheredto the inner surface of anode l opposite the intercell contact area.

In accordance with the invention, a protective coating 14 is applied toone entire surface of the magnesium anode 1, ex-

0 cepting only the central portion which is left exposed for makingintercell electrical contact. The coating comprises a Thin, dense layerof inert material which substantially excludes water molecules frompenetrating to the covered surface of the magnesium anode. A suitablematerial for this purpose is an epoxy primer paint. A suitable material,specified by way of example, is that presently commercially known asEpoxy-Cote primer 15-404 with curing agent 15-014, manufactured bySpeed-O-Laq Products Company, Inc. Other primer-type paints and hot meltadhesive materials have been found to be satisfactory. As is indicatedin FIG. 1 and shown in FIG. 2, the protective coating extends inwardlyunder the seal 10 to approximately the area which is eventually coveredby the intercell connecting material 12.

It has been found that use of the protective coating for the externalsurfaces of the magnesium anodes effectively prevents deterioration ofthe normally excellent electrical contact at the intercellconnector-anode interface.

When the several component parts of the cell are brought together andsealed within the film enclosure, the cell is ready for use in buildingmulticell batteries. The conductive wax or other intercell connectingmaterials fill the holes provided for access to the anode and currentcollector and electrically connect with the latter components.Advantageously, a metal foil moisture barrier 15 is interposed betweenadjacent cells. The blocks of cells may then be coated and/or insertedin containers and external terminals provided, all in known manner.

Iclaim:

1. In a dry cell comprised of flat cell elements including a magnesiumanode and enclosed within a film wrapper having at least one holetherein exposing a limited contact area of the exterior surface of theanode and seal means for closing the cell hole in the wrapper, theimprovement wherein the seal means comprises a coating on the anodecovering all of area said exterior surface of said anode surroundingsaid contact area and a body of sealing material surrounding the hole inthe wrapper and disposed between and adhering to said coating and saidwrapper, said coating comprising a water impervious material whichexcludes water molecules from said exterior surface of said anode andextending under and beyond said body of sealing material whereby theseal is effected between said coating and said film wrapper.

2. Structure in accordance with claim 1 wherein said anode contact areaand a hole in said wrapper are located centrally of said anode and theentire exterior surface of said anode except said contact area iscovered by the water-impervious coating.

3. Structure in accordance with claim 1 and including an intercellconnector comprising a body of electrically conductive thermoplasticmaterial adherently engaging and covering said contact area andprojecting through said hole in said wrapper.

4. In a dry cell comprised of flat cell elements including a magnesiumanode and enclosed within a film wrapper having a hole therein exposinga limited contact area at the center of the external surface of theanode and seal means for closing the cell at the hole in the wrapper,the improvement wherein the seal means comprises a coating on the anodecovering all of the exterior surface of the anode except the contactarea thereof, said coating comprising an epoxy primer paint which iswater impervious and excludes water molecules from said exterior surfaceof said anode, and a body of sealing material surrounding the hole inthe wrapper between and adhering to said coating and the wrapper.

UNITED STATES PATENT OFFICE CERTHHCATE QF CORRECTHNN 3,634,142 DatfliJanuary ll, L212 Lloyd W. Eaton Patent No.

Invent0r(s).

It is certified that error appears in the above-identified patent andthat said Letters Patent are hereby corrected as shown below:

Col. 2, line 11 "Thin" should be thin Col. 2, line 43 (Claim 1) DeleteareaP.

Signed and sealed this 31st day of October 1972 (SEAL) Attest:

USCOMM'DC 60376-F'69 U.5. GOVERNMENT PRINTING OFFICE: I969 O-365'334FORM PO-105O (10-69)

2. Structure in accordance with claim 1 wherein said anode contact areaand a hole in said wrapper are located centralLy of said anode and theentire exterior surface of said anode except said contact area iscovered by the water-impervious coating.
 3. Structure in accordance withclaim 1 and including an intercell connector comprising a body ofelectrically conductive thermoplastic material adherently engaging andcovering said contact area and projecting through said hole in saidwrapper.
 4. In a dry cell comprised of flat cell elements including amagnesium anode and enclosed within a film wrapper having a hole thereinexposing a limited contact area at the center of the external surface ofthe anode and seal means for closing the cell at the hole in thewrapper, the improvement wherein the seal means comprises a coating onthe anode covering all of the exterior surface of the anode except thecontact area thereof, said coating comprising an epoxy primer paintwhich is water impervious and excludes water molecules from saidexterior surface of said anode, and a body of sealing materialsurrounding the hole in the wrapper between and adhering to said coatingand the wrapper.